Amplifier tube for high frequencies



G- LIEBMANN AMPLIFIER TUBE FOR HiGK-FREQUENCIES unezs, 1949.

Filed July 29, 1945 Q v n "illz! d I I? r/alliii INVENTOR.

Gerhard Lie lnng'nn ATT RN EYS Patented June 28, 1949 2,474,584 AMPLIFIER TUBE FOR HIGH FREQUENCIES Cambridge, England, as-

Gerhard Liebmann,

Application signor to Cathodeon Limited, Cambridge, England, a. British company July 29, 1946, Serial No. 687,022

In Great Britain November 20, 1941 12 Claims. 1

v The invention refers to improvements in certain types of amplifier tubes for high frequencies in which the output load is connected between the control electrode or grid of the tube and the anode, and the high frequency modulation is applied to the cathode. Such tubes, sometimes called grounded grid triodes require a higher input driving power owing to increased input loading and have a lower gain than ordinary tubes of similar construction, but they are more stable in operation if proper screening is provided and possess a lower noise lever, probably due to the absence or reduction of induced noise.

A construction of this type of tube has been used in which the cathode, the grid and the anode form substantially plane surfaces perpendicular to the axis of the tube and parallel to each other. Although tubes made according to this design are operating sucessfully, they are very difficult to construct. The main reason for the diificulty seems to be that it is not easy to adjust the distances between the electrodes with the required accuracy, that the grid and cathode are liable to mechanical distortion which produces changes in the tube characteristics, and that thermal expansion of the electrodes in operation changes the tube parameters.

These disadvantages are avoided to a considerable extent in a tube constructed according to the present invention. At the same time, the proposed improved easily to the methods of mass production.

An amplifier tube according to the invention has concentric electrodes of circular, elliptical, rhomboidal or other suitable cross-section disposed coaxially in the tube envelope and comprising a cathode next surrounded by a grid electrode which is in turn surrounded by a plate electrode or anode, said grid electrode next to the cathode having electrostatic shields conductively secured thereto which are disposed so as to shield the anode and its lead-in wire from the cathode and its lead-in wire.

In constructing a tube embodying the invention, the said grid electrode next to the cathode, which serves as the control grid of the tube when in operation, is mounted on and conductively secured to a metallic grid shield which screens the input and output circuit elements from each other, and may be continued outside the tube enveconstruction lends itself lope to form part of the screening between the input and output circuits. In some constructions the entire electrode structure is mounted on this grid shield. This internal grid shield may consist of a disc-like member extending perpendicularly to the axis of the electrode structure and to the axis of the tube envelope. The cathode and anode leads may be taken out at opposite ends of the envelope and this disc-like member may be conductively secured to an annular metal plate sealed through the wall of the tube envelope perpendicularly to the axis of the electrode structure and so dividing the input and output sides of the tube. Alternatively, this disc may be associated, or combined in an integral structure, with a tubular screening member which surrounds the input leads, or the electrode structure, or both. For example, the disc may have 2. depending flange or skirt, or be conductively secured to a further tubular screen member forming such a skirt, which surrounds the input leads; or the disc may be conductively secured to a screening cylinder which extends upwardly above the disc so as to surround the electrode structure, which cylinder may also extend below the disc to form a skirt thereto surrounding the input leads, as previously mentioned, so that the disc in this case forms a partition across the cylinder. The anode and cathode leads may, in an alternative arrangement, be brought out at the same end of the tube envelope, in which case the disc-like grid shield may be formed or provided with a part extending between these leads so as to screen them from each other.

The electrode structure is kept in proper alignment by ceramic spacersor mica end plates in a way well known. The bottom mica plate is fixed to the aforementioned grid shield disc by means of rivets or lugs. The screening of the input circuit elements from the output circuit elements is completed by placing a screening cap over the top of the cathode, which sometimes projects slightly through the top mica plates, and connecting this cap to the grid backing or support wires.

The co-axial arrangement of the tube electrodes as described prevents any appreciable change of electrode spacing or alignment through thermal expansion, as the expansion takes place chiefly in the direction of the axis. The lateral expansion under the action of heat is only very slight. As all the electrodes are kept in proper alignment by the mica spacers and a symmetrical arrangement is used, the alignment can be achieved and maintained with great accuracy and the assembling of the complete electrode structure can be entirely separated from the sealingin process. Another advantage of the use of tubular electrodes is their greater mechanical strength. The ratio of length of electrode structure to its diameter depends on the use to which this typewq itube is put. In mapy cases, particularly at very; hi h: frequencies the ratiowill be: rather small; say of the order of one, giving a rather squat structure. Usually, however, this ratio will be nearer to the values common in that art.

In some cases the mica end plates are kept in proper relation to each other by sccuring;them:

by means of rivets or eyelets --or lugs to the anode or to supporting wires fixed to the anode. In

this case the metallic grid shield haslto betprpre vided with depressions at the points wh'eremther anode support wires pass through the mica tom plate in order to avoid electrical contact and to decrease the stray capacity between grid and, anode. In other ;case s. ,t11e control grid may have to; support the tpp niicaplate and the, anode may, be kept its proper position atthelowerendby; an. ad i iqna imicash c n The invention is more; particularly concerned; with triodes, bu t if-a veryhigh ampli'fication fac; r s, r quirsdg n add enalf q ee r dtcan be. p a twe ncontro 'gsi and esr d. nr e o hectedi a he cen ral Jani r... a s t: le irect u r ht ol aset narheapnlied o t ti sl of ourse ,smundedigr h'l i ir ency. If; th s. uxili r an liskept a anqsitw Po e tial); ithresps ttecathcdep' th su lm a s. er. hee ihathe au ilia y .rsnt. very low- Q. ar idlthe intmda iqnpi.na tit onh s r mplgyedin orderthat theinr htienmarbe more, c ear:- 0 mentslheneorwfll 'h.e ;1 y. a -oi=;.exam ,la.withreferr accomhan lrzayvi s,. in,.WhiCh..- .7 asecth, VL QW o e. o strue: ionoi this 0 nih dYihatheinrent 9n--.

E's... .1 h'owse mc iiifed p hs ructi nl nwhichl he lectrodes ares ar ied; a; moulded. lass. base.

i ht-sho s... diagrammatically a plan..-Vie w -0i. h lstmctur shownin El .1; I

hewaameci h d. construction of, tube. for working. wi th resonan1; line, circuits.

Referrin to Eigtllth sshqws asto nded rid iode. in, whi hta, opper. annuluse 2.. ealed h' o h he sla senrelo a l dir d s h inhut an output circuits, The cgncentric electrode assen l un dcn ametal sateen Ii.which s larger hanthe. holein. h t ehherisqztthrou hwhich, the .ele o ssemh1 spasssdw nvthe. tube s; bei a sembled, he. em n, i ctln ar ies;h end... hiznor aw x ha hro h h m ium r; he mica; is s-5Q nd, fiasupppr a a ith vdel h An de he reen alas-Pro vided w haistepned .fom as shew,r inrt e11- hata the n e pnot ina wire heatin th euehithe ev r m ca isc 5.; shah; n-ptt o h-1 he. metal. screen. The top of the grid is closed by atscreen l. ma. can-9 .7 ansiza ha nodet eaih assesmathsp ih-bathe to ct h tubs nre eper ntrd r. to. her-able t orhssemhle tube, the. hol nw llet opper-,discl a ma e arger, than the; electrode. ass mbly sot ha .wlhenthe 1e tr.od

sembly has been mounted on the glass stem I l, the whole is inserted into the tube envelope. The screen 3 is conductively secured to the copper disc 2 by means of fixing lugs [2 depending from the disc 2 which pass through apertures or slots in the screen 3 and are twisted or bent over. Thereafter the stem H is sealed into the glass envelope l in the usual way and the tube base fitted.

A certain difliculty is sometimes encountered in the production of tubes according to the improvfldponstruetion. This diificulty arises from the :factthat it is not easy to shapeethez anode located rather near the disc shaped screen between input and output circuits in such a Way that it can be degassed by high frequency eddy currents without;glowingmnduly, and thus distorting the screen. This difiiculty can be overcome by selecting; -suitable-materials for the anode and for the ,di;sc. An improvement is brought about by making the disc from copper, only some inset to whichltheegridproper is fastened, and the anode itself; being] made from nickel. A further improye nentds achieved by using iron as the anode material, the screen being made entirely from nickel or copper. The combination of copper screen'andfiron anode-isthe-best one but is mostly not required; The--irpnanode may, be made. froma non-rusting-iren alloy of highpermeabil ity or-the iron anode may be nicl 1;plated to prevent-it from rusting during the production process;

Figures 2 and-3 showa modifiedjconstruction, in whichthe electrodestructure' is supported by an moulded glass-b1ase [4* having se aledi through, lead-in: pins. The electrode assembly is similar to -that shown in'Fig; 1 'and -is --similarly, mounted? onthe dise-shaped-grid shield 3a securedto the grid-a4. Inthis-embodiment however, the electrode leadsa-re all-tal en through the mo ulded glass base 14; and the shield"3a;.is;,bent to form a depending-flange portion 311 which; extends between the anode; leadj-in pin l3 and fthe. rest: 01f theleads; In-some cases it is found advantageous to; employa double-lead forytheabode i order to'reduce lead inductance, to which end the anode may; be connected to two-such leaddn pins as l-3y'which, aswill-,be understood; ,are disposed at' the--same;side'ofthe-fiange 3b; The. shield 3a is-con -ductivel-y, secured 'by its ,fi'ange 3 b; toone or; more (conveniently two of the lead -in pins a s, indicated at' l5; whereby th'e electrode assembly. oun n, he. hie hrnqor i v A li he 1ead=in.ni ame st pin U011 h c thode ins, I 1;. l flj'for the cathode. heater, pin or pins I 5 for he. g ith its: hield; a in, r s, 3 or the delm he. l'l'finifidfifl. a i clev ar: heherinh r i i he hqul e ela s ase. 4. A1= er atiilel ,th a a ho eudits. heater ma he nn t d c eadei inssr uned o ther withnhhd qhe rthesentre of... a. circular. rran em nt; n eade n ins Qwhi htheo her electrodes are. onnected-i h scre n n .provided-b e; sh e d: 11. be n ihue lfloutside the. ube env lope y. externah creena if: desi ed,

n t ad:. 't ki sl, heanode lea hrough he mou ded lasshase I tithe anode leadmayv hev taken through the top end of thejubeenyelop e, asin. the. mhQdimeht HEia Inthiscas th disczshaped grid jshield. 3alwouldn t ,ne t be. ent d ormlt e flanselpprt pn, b; s rev us m escribed. ut...may, howev rhbe associated, omhinedin an.int xallstructure.with a tubules; heming; mem er which; urrounds the nput; adslnrl h l et ode.assemhlnon tht Th s,-

the disc 3a may, for example, be formed with a depending tubular flange or skirt, or be conductively secured to a further tubular screen member forming such a skirt, which surrounds the input leads. Such tubular screen member may be a cylinder which also extends upwardly above the disc 3a so as also to surround the electrode assembly, the disc 3a thus forming a partition across the cylinder. The anode lead taken through the top of the tube envelope may be brought out as a single wire, or as a double wire to reduce lead inductance. Alternatively, in a construction intended to work with resonant line circuits, the lead-in wire or wires for the anode may be replaced by a metal tube sealed through the glass wall of the envelope or to the glass in a manner known per se or as described in British Patent No. 553,350, this tube being closed at its lower end or at another point by a diaphragm and being connected to the anode by means of a spring clip formed by tongues fixed to the top end of the anode. This metal tube may be sealed to the envelope before being pushed into the anode clip. Further, an exhaust tube may be provided which is sealed to the anode lead-in tube and is covered, after exhaust and sealing-off, by an external extension of the tube, as described in the above-mentioned patent.

Fig. 4 shows a modified construction for working with concentric line resonators. A copper annulus 21 is sealed through the wall of the tube envelope 29 and separates the input and output circuits of the tube. Also sealed through the Wall of the envelope are two annular flanged copper members 22 and 23 arranged as shown. The upper member 22 carries the anode 24 (and may be made integral therewith) and the lower member 23 carries the cathode 25. The grid 26 is carried by the screen 2'! which is secured to the copper annulus 2| by eyelets or twisted lugs 28. The upper end of the grid is closed by the screening cap 29 and the electrodes are spaced by mica washers 30 in well-known manner. The aperture in the centre of the member 23 is made sufiiciently large to allow the screen 21 to pass therethrough during assembly.

The inner conductors of the concentric line circuits are constituted by metal cylinders 3|, 32 which are a push fit on or inside the flanges of the members 22, 23 respectively. The outer I conductors of the lines are also constituted by metal cylinders 33 and 34 which are insulatingly supported on opposite sides of the grounded copper screen 2|. The tuning of the resonant lines is effected by annular plungers 35, 36 sliding within the pairs of tubes 3|, 33 and 32, 34, respectively.

I claim:

1. An amplifier tube having an envelope, concentric electrodes disposed coaxially in said envelope, said electrodes including a cathode next surrounded by a grid electrode and an anode surrounding said grid electrode, said grid electrode next to said cathode being conductively mounted by one end thereof on a metal screening annulus sealed through the wall of said envelope substantially perpendicularly to the axis of said envelope, the other end of said grid electrode being closed by a metal screening cap conductively secured thereto, a flanged metal member sealed through said envelope wall substantially parallel to said screening annulus and electrically connected to said cathode, with the flange of said member disposed outside said envelope.

2. An amplifier tube as defined in claim 1,

wherein said flanged metal member supports said cathode.

j 3. 'An amplifier tube as defined in claim Land further comprising a metallic tube fitting said flange of said flanged metallic member, and constituting an internal conductor of a concentric resonant line.

4. An amplifier tube as defined in claim 1, and further comprising a metallic tube fitting said flange of said flanged metallic member and constituting the-internal conductor of a concentric resonant line, and a metal cylinder surrounding said metallic tube and constituting the external conductor of said resonant line, an end of said outer metal cylinder lying adjacent to but insulated fromsaid metal screening annulus.

"*5. An amplifier tube having an envelope, concentric electrodes disposed coaxially in said envelope, sa'id electrodes including a cathode next surrounded by a grid electrode and an anode surrounding said grid electrode, said grid electrode next to said cathode being conductively mounted by one end thereof on a metal screening annulus sealed through the wall of said envelope substantially perpendicularly to the axis of said envelope, the other end of said grid electrode being closed by a metal screening cap conductively secured thereto, a flanged metal member sealed through said envelope wall substantially parallel to said screening annulus and electrically connected to said anode, with the flange of said member disposed outside said envelope.

6. An amplifier tube as defined in claim 5, wherein said flanged metal member supports said anode.

7. An amplifier tube as defined in claim 9, and further comprising a metallic tube fitting said flange of said flanged metallic member, and constituting an internal conductor of a concentric resonant line.

8. An amplifier tube as defined in claim 5, and further comprising a metallic tube fitting said flange of said flanged metallic member and constituting the internal conductor of a concentric resonant line, and a metal cylinder surrounding said metallic tube and constituting the external conductor of said resonant line, an end of said outer metal cylinder lying adjacent to but insulated from said metal screening annulus.

9. An amplifier tube having an envelope, concentric electrodes disposed coaxially in said envelope, said electrodes including a cathode next surrounded by a grid electrode and an anode surrounding said grid electrode, said grid electrode next to said cathode being conductively mounted by one end thereof on a metal screening annulus sealed through the wall of said envelope substantially perpendicularly to the axis of said envelope, the other end of said grid electrode being closed by a metal screening cap conductively secured thereto, two flanged metal members sealed through said envelope wall substantially parallel to said screening annulus and at opposite sides thereof, one of said members being electrically connected to said cathode and the other of said members being electrically connected to said anode, the flanges of both said members being disposed outside said envelope.

10. An amplifier tube as defined in claim 9, wherein said flanged metal members respectively support the electrodes to which they are connected.

11. An amplifier tube as defined in claim 9, and further comprising two aligned metallic tubes at opposite sides of said screening annulus, which 

